A temperature sensor using a thermosensitive element (thermistor element) of which a resistance value changes depending on temperature is known as a temperature sensor that measures the temperature of exhaust gas of an automobile and the like.
The temperature sensor includes a thermosensitive element, an electrode wire, a sheath pin, and a protective layer. The thermosensitive element is composed of an oxide, such as Y2O3.Ycr/MnO3. An electrode film composed of Pt or the like is provided on the surface of the thermosensitive element. The electrode wire composed of Pt or the like is connected to the electrode film. The sheath pin includes therein a signal wire electrically connected to the electrode wire. The protective layer has a two-layer structure composed of a glass mold covering the thermistor element (refer to JP-A-2009-115789).
The temperature sensor configured in this manner has the thermosensitive element composed of an oxide, as described above. Therefore, in a temperature sensor that is used under reductive conditions, such as for measurement of the exhaust gas temperature of an automobile, the two-layer structure protective layer is formed as described above from the perspective of preventing reduction degradation of the thermosensitive element and reducing internal stress.
However, when the protective layer is formed having a two-layer structure, the configuration of the temperature sensor becomes complicated and manufacturing cost increases.
In addition, in the temperature sensor having the above-described conventional configuration, the electrode film composed of platinum Pt is formed on the thermosensitive element. Therefore, the signal wire within the sheath pin and the electrode film are connected by an interconnecting electrode wire composed of Pt. However, because platinum Pt is used, manufacturing cost increases.
In addition, for use in temperature measurement of exhaust gas and the like, the temperature sensor may be set near an internal combustion engine. In this instance, large vibrations from the internal combustion engine are easily transmitted to the temperature sensor. As a result, the thermosensitive element of the temperature sensor may vibrate, and the bonding section between the thermosensitive element and the electrode wire may become disconnected. In particular, disconnection easily occurs in the electrode wire composed of platinum Pt.
In light of the above-described circumstances, a thermosensitive element using a wide-range thermistor material has been receiving attention in recent years (refer to JP-A-H08-273904). The thermosensitive element is configured by a first phase and a second phase. The first phase is composed of insulating matrix particles composed of a non-oxide. The second phase is composed of semiconductive or conductive particles dispersed discontinuously in the shape of a three-dimensional mesh in the first phase. The wide-range thermistor material such as this is composed of a non-oxide. Therefore, the thermistor material is not easily reduced even in a reducing atmosphere. A two-layer structure protective layer such as that described above is not required. Cost reduction of the temperature sensor can be achieved.